I’d really like the links. Thanks! This is all very new to me. I barely understood the difference between volts and amps before starting my research.
One thing I’m a little concerned about wrt charging a battery pack with BMS is that (as I understand) this typically involves using a cheap and dumb charger that doesn’t have any display indicating current state of charging and doesn’t switch itself off once the batteries are fully charged. I imagine clever ones are available as well but probably nowhere near the price range of the IMAX.
Oh hey you get what i mean!
Imagine charging with a BMS like charging your phone or laptop, it’s just plugging in and letting the BMS handle the rest. With a dedicated charger you can at least see the voltages of the individual cells once every cycle. If a cell goes bad and you are using a BMS there’s no way to tell except physical changes to the cell, like it puffing up or so.
2 years ago I didn’t know anything but after 3 builds and a lot of research I would call it “advanced knowledge”
What you describe is a power supply.
I’m talking about an Li-ion charger, it has all safety features including overcharge protection for the whole pack. The overcharge protection for each single cell is managed by the BMS. There is double safety.
You could use this 12s BMS for discharge, too so all cells are protected during usage as well (except over discharge).
As charger you could use any 50.4V Li-ion charger. There are the cheap “bricks” which get got during charging (like this 1.5A, couldn’t find a 2-3A brick now). What I use right now is this 4A charger which takes 2 hours to charge a 12s 8Ah lipo. It is plastic but small and has a fan so nothing gets hot. I personally don’t like these huge aluminium chargers.
The big sale on aliexpress starts in 6 days and you could get this 4A charger for 19€ with free shipping. I think I’ll buy this one in 6A again. But I have to mention that my charger came broke and I had to change the main power wire.
The last thing would be a waterproof charging port then you are ready to charge, no struggling…
I have a voltmeter attached to the BMS so I can see the voltage of the battery also during charging
Exactly, imagine you would have to open your phone or laptop everytime and take the batteries out for charging For me this is not an option…
Thanks again guys for all the info and the links. So I guess I can either go with the BMS and the 4A charger for about $55 in total (if everything is actually delivered and functional; I don’t have particularly good experience with these Chinese online stores). Or I could get two IMAXes and a power supply (maybe this one) for about 60 EUR. Not a big difference in price. I’m slightly inclined towards the without BMS solution for the reasons @Der6FingerJo mentioned – you have more control: display on the charger that tells you if something is wrong. With BMS, the BMS will try its best to make sure there won’t be a problem but if it is you’ll get no feedback. Plus, taking apart 4 batteries for charging isn’t that hard. Having 12x 1s would be a different story.
With BMS, on the other hand, the charging would be more convenient (no need to take the battery pack apart) and also about 2 times faster (hm, that’s actually significant). I also wouldn’t need that many connectors. I could just solder it all together (if I learn how to do it and get myself something to do it with … which seems inevitable anyway).
At last I decided to go without the BMS solution. Seems cleaner and more modular. With the XT150 connectors I can easily wire up the batteries any way I want (not that I have a particular use case for that, but I like the flexibility ).
Going with two cheap IMAX B6 chargers (yeah, not even the genuine ones ). There’s a youtube video from a guy who has both the genuine and the copy and says he doesn’t see any difference. With two, I can charge the battery pack in about 3.5 hours, which is not too bad. Plus, slow charging is good for the batteries anyway, isn’t it?
Here’s my HobbyKing shopping list. I believe I have everything except for ESC (waiting for ESCape) and power supplies (will probably buy some used ones locally). Is there something else you would recommend throwing in? Thanks!
Must say that one is just awesome with a 24v power supply.
4x 8000 mah balance charged under 2 hours.
May already be too late, but would get 4x 6s due to te range. 8000 mah is around 8 km off-road with hills. If that’s enough, go for it. If you lack the cash, I’d still go for 2x 6s 8000mah…otherwise you’ll end up with a shitload of lipos on your deck when you do decide to increase range.
@telnoi You mean 8000 mah 6s, right? Not 12s? From what I have read, people are getting about 10 Wh/km on road with a skateboard and 20 Wh/km off road with a MTB. I’ll mostly do MTB on road so I suppose to end up somewhere inbetween (15 Wh/km?).
8000 mah 12s LIPO is 352 Wh, so that should be good for about 17 km off-road. 17 km is exactly the range I need, but since I’m going to mostly do on road I hope to get more than that and have some padding.
Depends on where and how you ride I guess. In my case, 8000 mah 10S is discharged to 3.7V in around 8 km. For you, that number might be different. Half of my journey is uphill, with partial mud plowing, etc.
Once you get used to MTB, you’ll most likely want to go further and faster relatively soon. The prospect of having 8 lipos + all the wires is rather unpleasant.
My current range with 16000 MAH 10S is good for around 17 km. You might get a bit more out of it using 12S.
I see. Thanks for the warning. I’ll go with the 4x 3s anyway. The extra cost for 2x 6s just seems too much. I believe it will currently be OK for my use case. If I need more range, there’s a number of options. I could either double up the battery and deal with 8 LIPOs (probably convert to BMS then) or change the battery pack completely (I’m hoping 3s might be easier to sell off than 6s) or maybe just get 2 extra batteries and convert to 9s (2x 3x3s).
Do you already need a oxygen mask on your rides?
Jesus, this must be serious uphill action with this consumption , no heat problems?
With the old setup I only tried once to climb a hill but the motors got sizzling hot and the vescs reached temp limits, my MTB felt like a old lame horse the whole ride.
My voltage drops and stays down for 1v after I am done with one climb. That’s with 16000. I go up there almost full throttle/about 28 km/h. In fact, some off-road sections I need to be full throttle to make it walking speed. That’s with 149kv. With all that, my motors are Luke warm. My focboxes do overheat sometimes, crawling to a halt completely.
The roads here are used by heavy machinery. Those foresters often repair the sand roads with big stones, so the board never rolls smoothly. There is always a massive loss of energy and momentum.
My hope is direct drive and the trampa will improve efficiency a bit. Different gear ratio. Also need to work on a waterproof enclosure with proper cooling.